Wave transformation method and device

ABSTRACT

The present invention relates a waveform transformation method and apparatus. It uses multilevel transformation module in series, and the output voltages of power modules at all levels are superposed to get the total output voltage, whereas each power transformation module realizes AC-to-AC direct conversion. The deviation between the output voltage and setting reference voltage at any time point is made as small as possible by selecting different transformation modules as current working circuit and selecting output voltage waveform of the each different transformation modules. The invention includes outputting n groups of electrical insulating AC and n transformation modules connected with AC. The wave transformation method and device of present invention eliminates the intermediate DC stage, so that the circuit is greatly simplified, the cost is reduced obviously. and improve working efficiency. It makes voltage and current harmonics to be reduced and obtains higher power factor.

FIELD OF INVENTION

[0001] The present invention is related to a wave transformation methodand device in high voltage switch field. More particularly, thisinvention is related to a variable-frequency drive or variable-frequencypower supply for motors.

BACKGROUND OF INVENTION

[0002] Frequency converters and variable-frequency power supplies arewidely used as driving units for AC (alternating current) motors and soon, and most of them employ AC-AC conversion or AC-DC (direct current)conversion mode. The existing technology for AC-AC frequency convertersutilizes direct AC-AC conversion and output Volt Alternating Current(VAC) through altering the triggering angle of a switch component. Sucha solution achieves a relative low power factor and may result in heavyharmonic wave pollution to the electric network and electric devices. Onthe other hand, the existing technology for voltage-type AC-DC-ACgeneral-purpose frequency converters employs pulse-width modulation(PWM) method (i.e., perform switching control of intermediate DC voltagewith a semiconductor switch component) to output VAC. Such a solutionincreases equipment cost and decreases working efficiency of equipmentdue to existence of the intermediate DC stage. Above problems are moresevere in high capacity frequency converters and variable-frequencypower supplies.

DESCRIPTION OF INVENTION

[0003] The object of the present invention is to provide a wavetransformation method and device which eliminate the intermediate DCstage in order to reduce the cost of the device and improve workingefficiency, and it is still a further object of the preset invention toprovide a wave transformation method and device to delivers smallervoltage harmonics and higher power factor.

[0004] The AC-AC wave transformation device in the present inventioncomprises n transformation modules. The input terminals of thosetransformation modules are connected to n groups of electricalinsulating AC. Each group has m phases. The output ends of thosetransformation modules are connected in series to form a total voltageoutput. Each of those transformation modules further comprises powersemiconductor switch components or power semiconductor switch componentgroups to form a bi-directionally controllable m-phases rectificationcircuit, the output polarity of which is variable.

[0005] The transformation module in the device is a full-wavebi-directionally controlled m-phases rectifying circuit whose outputpolarity is variable. The full-wave bi-directionally controlled m-phasesrectifying circuit consists of power semiconductor switching componentsor power semiconductor switching component groups connected. Thefull-wave bi-directionally controlled m-phases rectifying circuitconsists of 2×m power semiconductor switching components or powersemiconductor switching component groups. Each of power semiconductorswitching components or power semiconductor switching component groupsis connected respectively between m input lines and two output lines.

[0006] The transformation module in the device can also be a half-wavebi-directionally controlled m-phases rectifying circuit whose outputpolarity is variable. The half-wave bi-directionally controlled m-phasesrectifying circuit consists of power semiconductor switching componentsor power semiconductor switching component groups connected. Thehalf-wave bi-directionally controlled m-phases rectifying circuitconsists of m+1 power semiconductor switching components or powersemiconductor switching component groups, wherein m power semiconductorswitching components or power semiconductor switching component groupsare connected respectively between m input lines and output lines; andone power semiconductor switching component or power semiconductorswitching component group is connected respectively between the inputneutral line and output line.

[0007] The transformation module in the device is a bi-directionallysemi-controlled m-phases rectifying circuit whose output polarity isvariable. The bi-directionally semi-controlled m-phases rectifyingcircuit consists of power semiconductor switching components or powersemiconductor switching component groups connected. The bi-directionallysemi-controlled m-phases rectifying circuit consists of 2×m powersemiconductor switching components or power semiconductor switchingcomponent groups, each of which is connected respectively between minput lines and two output lines.

[0008] The power semiconductor switching components in the device arebi-directional thyristors.

[0009] The power semiconductor switching component groups in the deviceare either unidirectional thyristors which are positive-negativeconnected in parallel, or IGBTs which positive-negative are connected inseries, or turn-off thyristors which are positive-negative connected inparallel, or IGCTs which are positive-negative connected in parallel, orturn-off thyristors which are positive-negative connected in series, orIGCTs which are positive-negative connected in series.

[0010] The AC-AC waveform transformation method of the present inventionincludes the following steps:

[0011] 1} setting a sine-wave voltage to be output, and dividing thesine-wave according to time interval t0, t1, t2, t3 . . . ti , andselecting the voltage waveform during t0˜t1 as the given referencevoltage;

[0012] 2} selecting j groups from the n groups of m phases AC powersupply that are electrically insulated to each other as the presentinput voltage, where j≦n;

[0013] 3) performing bi-directionally controllable rectification on therest (n-j) groups m phases AC, so that its output voltage is 0;

[0014] 4) for the selected j groups of m phases AC which areelectrically insulated each other, selecting one voltage waveform foreach group from all voltage waveforms output during t0˜t1 after carryingout bi-directionally controllable rectification on j groups of m phasesAC voltage so that j voltage waveforms are obtained by performingbi-directionally controllable rectification on j groups of electricalinsulating m phases AC;

[0015] 5} finding the sum of above-mentioned j voltage waveforms to geta total calculated output voltage;

[0016] 6} comparing the calculated output voltage during t0˜t1 with theabove-mentioned given reference voltage; selecting m phases AC powersupplies of different groups from the above-mentioned n groups of mphases AC that are electrically insulated to each other as current inputvoltages; among the m-phase AC power supply of each group, selectingdifferent voltage waveforms that have gone through bi-directionallycontrollable rectification, so that the difference between thecalculated output voltage and given reference voltage is made as low aspossible at any time, and the total harmonics in the output voltage ismade the smallest or some high-order harmonics is made as low aspossible, or the total harmonics in the sum of current for n groups ofAC power supplies is made the smallest or some high-order harmonics ismade as low as possible; or the average leading or lagging power factorsof each in the n inputting groups is made as large as possible;

[0017] 7} determine the working status of each bi-directionallycontrollable rectifying circuit based on the voltage waveformcorresponding to each selected m-phase AC power supply, and performingbi-directionally controllable rectification in accordance to the workingstatus determined in above way;

[0018] 8} selecting the given expected voltage waveforms during t1˜t2,t2˜t3, ti−1˜ti as given reference voltages respectively and repeat step2˜8, and obtain the desired AC output voltages.

[0019] In above mentioned method, the n groups of m phases AC powersupply that are electrically insulated to each other and is obtained byway of insulated transformation or insulated phase-shift transformationof a total AC power supply.

[0020] The wave transformation method and device of present inventioneliminates the intermediate DC stage, so the circuit is greatlysimplified, therefore it can reduce the cost and improve workingefficiency, deliver smaller voltage and current harmonics and higherpower factor.

DESCRIPTION OF FIGURES

[0021]FIG. 1 is the circuit diagram of the device of present invention.

[0022]FIG. 2 is the full-wave bi-directionally controlled rectifyingcircuit included in the transformation module of the device of presentinvention.

[0023]FIG. 3 is the half-wave bi-directionally controlled rectifyingcircuit included in the transformation module of the device of presentinvention.

[0024]FIG. 4 is the bi-directionally semi-controlled rectifying circuitincluded in the transformation module of the device of presentinvention.

[0025]FIG. 5 is the bi-directionally controlled rectifying circuitconsisting of bi-directional thyristors.

[0026]FIG. 6 is the bi-directionally controlled rectifying circuitconsisting of thyristors.

[0027]FIG. 7 is the bi-directionally semi-controlled rectifying circuitconsisting of turn-off IGBTs.

[0028]FIG. 8 is the full-wave bi-directionally controlled rectifyingcircuit consisting of turn-off IGBTs.

[0029]FIG. 9 is the full-wave bi-directionally controlled rectifyingcircuit consisting of turn-off thyristors or IGCTs in series.

[0030]FIG. 10 is the full-wave bi-directionally controlled rectifyingcircuit consists of turn-off thyristors or IGCTs in parallel.

[0031]FIG. 11 is the sine-wave voltage to be output.

[0032]FIG. 12 is an output voltage waveform selected forbi-directionally controlled rectifying circuit.

[0033]FIG. 13 is the second output voltage waveform selected.

[0034]FIG. 14 is the third output voltage waveform selected.

[0035]FIG. 15 is the fourth output voltage waveform selected.

[0036]FIG. 16 is the overlapped output voltage waveform

[0037]FIG. 17 is an example of the device of present invention, wherein,1 indicates first-grade transformation module; 2 indicates second-gradetransformation module; 3 indicates third-grade transformation module; 4indicates fourth-grade transformation module; 5 indicates fifth-gradetransformation module; 10-19 indicates thyristors forming thebi-directionally controlled rectifying circuit

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0038] The principle of the present invention and the working process ofthe device will be described in detail below in connection with attachedfigures.

[0039]FIG. 1 is the circuit diagram of the device designed by presentinvention. Referring to FIG. 1, the input terminals of transformationmodule 1, transformation module 2 . . . transformation module N areconnected respectively with input AC power supplies V11, V21, . . . VM1;V12, V22, . . . VM2; V1N, V2N, . . . VMN, and the output terminals oftransformation module 1, 2 . . . M are connected in series so that atotal output voltage VO is produced.

[0040]FIG. 2 is the full-wave bi-directionally controlled rectifyingcircuit included in the transformation module of the device of presentinvention. Referring to FIG. 2, the switching component K1, K2, . . .Km, Km+1, Km+2, . . . K2 m are connected to form a full-wavebi-directionally controlled m phases rectifying circuit. Each powersemiconductor switching component or power semiconductor switchingcomponent group is connected respectively between m input lines and twooutput lines, their input terminals are connected to m-phase AC voltageV1, V2 . . . Vm, the output voltage is VO.

[0041]FIG. 3 is the half-wave bi-directionally controlled rectifyingcircuit included in the transformation module of the device of presentinvention. Referring to FIG. 3, the switching component K1, K2, . . .Km, Km+1 are connected together to form a half-wave bi-directionallycontrolled m phases rectifying circuit, their input terminals areconnected to m-phase AC voltages V1, V2, . . . Vm and neutral line N,where, m power semiconductor switching components or power semiconductorswitching component groups are connected respectively between m inputlines and output lines, one power semiconductor switching component orpower semiconductor switching component group is connected between theinputting neutral line and output line, the output voltage is VO.

[0042]FIG. 4 is another circuit structure in the transformation moduleof the device of present invention. Referring to FIG. 4, each switchingcomponent includes a diode and a switch, the switching component K1, K2,. . . Km, Km+1, Km+2, . . . K2 m are connected together to form abi-directionally semi-controlled m phases rectifying circuit, each powersemiconductor switching component or power semiconductor switchingcomponent group is connected respectively between m input lines and twooutput lines, their input terminals are connected to m-phase AC voltageV1, V2, . . . Vm, the output voltage is VO.

[0043]FIG. 5 is the circuit diagram of the transformation moduleconsists of bi-directional thyristors. Referring to FIG. 5,bi-directional thyristor K1, K2, . . . Km, Km+1, Km+2, . . . K2 m areconnected together to form a bi-directionally controlled m phasesrectifier-bridge circuit, each power semiconductor switching componentis connected respectively between m input lines and two output lines,their input terminals are connected to m-phase AC voltage V1, V2, . . .Vm, the output voltage is VO.

[0044]FIG. 6 is the circuit diagram of the transformation moduleconsists of unidirectional thyristors. Referring to FIG. 6, eachswitching component includes two thyristors connected reversely inparallel, the switching component K1, K2, . . . Km, Km+1, Km+2, . . . K2m are connected together to form a bi-directionally controlled m phasesrectifying circuit, each power semiconductor switching component groupis connected respectively between m input lines and two output lines,their input terminals are connected to m-phases AC voltage V1, V2, . . .Vm, the output voltage is VO.

[0045]FIG. 7 is the circuit diagram of transformation module consists ofIGBTs. Referring to FIG. 7, each switching component group includes oneIGBT and two diodes, and after the IGBT is connected to a diode inseries, it is connected in series to another diode. The switchingcomponent formed in this way K1, K2, . . . Km, Km+1, Km+2, . . . K2 mare connected to form a bi-directionally semi-controlled m phasesrectifying circuit, each power semiconductor switching component groupis connected respectively between m input lines and two output lines,their input terminals are connected to m-phases AC voltage V1, V2, . . .Vm, the output voltage is VO.

[0046]FIG. 8 is the circuit diagram of transformation module consists ofIGBTs. Referring to FIG. 8, each switching component group includes twoIGBTs which are connected reversely in series each other, the switchingcomponent formed in this way K1, K2, . . . Km, Km+1, Km+2, . . . K2 mare connected to form a bi-directionally controlled m phases rectifyingcircuit, each power semiconductor switching component group is connectedrespectively between m input lines and two output lines, their inputterminals are connected to m-phases AC voltage V1, V2, . . . Vm, theoutput voltage is VO.

[0047]FIG. 9 is the full-wave bi-directionally controlled rectifyingcircuit consists of turn-off thyristors or IGCTs in series. Referring toFIG. 9 each switching component includes two bi-directional thyristorsor IGCTs which are connected reversely in series each other, theswitching component formed in this way K1, K2, . . . Km, Km+1, Km+2, . .. K2 m are connected to forme a bi-directionally controlled m-phasesrectifying circuit, each power semiconductor switching component groupis connected respectively between m input lines and two output lines,their input terminals are connected to m-phases AC voltage V1, V2, . . .Vm, the output voltage is VO.

[0048]FIG. 10 is the full-wave bi-directionally controlled rectifyingcircuit consists of turn-off thyristors or IGCTs in parallel. Referringto FIG. 10, each switching component group includes two bi-directionalthyristors or IGCTs which are connected reversely in parallel eachother, the switching component formed in this way K1, K2, . . . Km,Km+1, Km+2, . . . K2 m are connected to form a bi-directionallycontrolled m-phases rectifying circuit, each power semiconductorswitching component group is connected respectively between m inputlines and two output lines, their input terminals are connected tom-phases AC voltage V1, V2, . . . Vm, the output voltage is VO.

[0049] The power semiconductor switching component group in the deviceof present invention can also consist of one or more field effecttransistors, IGCTs, IGBTs, MCTs, SITs; or consist of one or more fieldeffect transistors, IGCTs, IGBTs, MCTs, SITs and one or more diodes.

[0050] The process of waveform transformation designed in presentinvention will be described in detail below. To make it clear, we takethe embodiment circuit in FIG. 17 as example.

[0051]FIG. 11 is the waveform of expected value for given outputsine-wave voltage, and it is divided into parts according to time t0,t1, t2, t3, First, the given expected voltage waveform during t0˜t1 ofFIG. 8 is selected as the given reference voltage.

[0052] The bi-directionally controlled rectifying circuit oftransformation module 1, 2, 3 and 4 in FIG. 17 is selected as currentworking circuit, and turn on thyristor 16, 17, 18 and 19 in thebi-directionally controlled rectifying circuit of transformation module5, so that bi-directionally controlled rectifying circuit 5 is underno-working state.

[0053] Next, the output voltage waveform for bi-directionally controlledrectifying circuit of each transformation module is selected as currentworking circuit:

[0054] For the bi-directionally controlled rectifying circuit oftransformation module 1 in FIG. 17, the three-phase input voltages ofthe circuit respectively are assume as following:

va=uksin(ωt);

vb=uksin(ωt−2/3π);

vc=uksin(ωt−4/3π);

[0055] wherein,, uk is a constant.

[0056] For the different ON-OFF states of thyristors in the circuit, itmay corresponds to various output voltage, e.g. when thyristor 10, 14are turned on at ωt=t0, its output voltage waveform at t0˜t1 is (va-vb);when thyristor 11, 15 are turn on at ωt=t0, its output voltage waveformat t0˜t1 is (vb-vc); when thyristor 12, 13 are turn on at ωt=t0, andthyristor 14 is turned on at ωt=5/6 π, its output voltage waveform is(vc-va) (when ωt=t0˜5/6π) and (vc-vb) (when ωt=5/6π˜t1). The outputvoltage waveform selected for transformation module 1 in this example is(va-vb) (when ωt=t0˜2/3π) and (va-vc) (when ωt=2/3π˜t1) as shown in FIG.12, and the corresponding ON-OFF state of thyristors are: thyristor 10,14 are turned on at ωt=t0, and 15 is turned on at ωt=2/3π. With thismethod, the output voltage waveform for transformation module 2 as shownin FIG. 13, that for module 3 as shown in FIG. 14, and that for module 4as shown in FIG. 15 are selected.

[0057] The above selected output voltage waveforms for transformationmodule 1, 2, 3 and 4 are superposed to obtain the voltage waveform shownin FIG. 16. The waveform during time t0˜t1 is compared with the givenreference voltage during time t0˜t1 (as shown in FIG. 11), thedifferences at different points are low, and according to Fouriertransformation frequency analysis, the harmonic voltage in the output isat minimum, so it is taken as a group of an optimal output voltagewaveform finally selected. If the output harmonic voltage is notminimal, it is necessary to re-select the transformation module ascurrent working circuit or re-select the output voltage waveform of eachtransformation module.

[0058] Based on the optimal output voltage waveform for bi-directionallycontrolled rectifying circuit of each transformation module selectedaccording to above-mentioned way, ON-OFF state of each thyristor duringt0˜t1 is determined, and trigger signal is sent to each thyristor, hencethe desired output voltage Vo is obtained.

1. An AC-AC wave transformation device comprising n transformationmodules, characterized in that the input terminals of each of thesetransformation modules are connected to n groups of m phase AC that areinsulated from each other; the output terminals of these transformationmodules are connected in series to obtain a total voltage output; eachtransformation module consists of power semiconductor switchingcomponents or power semiconductor switching component groups, the powersemiconductor switching components or power semiconductor switchingcomponent groups are connected to form a bi-directionally controlled mphase rectifying circuit, the output polarity of said rectifying circuitis variable.
 2. The AC-AC waveform transformation device according toclaim 1, wherein the transformation module is a full-wavebi-directionally controlled m phase rectifying circuit, said full-wavebi-directionally controlled m phase rectifying circuit is formed byconnecting power semiconductor switching components or powersemiconductor switching component groups, the output polarity of saidfull-wave bi-directionally controlled m phase rectifying circuit isvariable, said full-wave bi-directionally controlled m phase rectifyingcircuit consists of 2×m power semiconductor switching components orpower semiconductor switching component groups, each of the powersemiconductor switching component or power semiconductor switchingcomponent group is connected respectively between m input lines and twooutput lines.
 3. The AC-AC waveform transformation device according toclaim 1, wherein the transformation module is a half-wavebi-directionally controlled rectifying circuit for m-phase AC, saidhalf-wave bi-directionally controlled rectifying circuit for m phase isformed by connecting power semiconductor switching components or powersemiconductor switching component groups, the output polarity of saidhalf-wave bi-directionally controlled m phase rectifying circuit isvariable, said half-wave bi-directionally controlled m phase rectifyingcircuit consists of m+1 power semiconductor switching components orpower semiconductor switching component groups, each of m powersemiconductor switching component or power semiconductor switchingcomponent group is connected respectively between m input lines andoutput lines, and one power semiconductor switching component or powersemiconductor switching component group is connected between the inputneutral line and output line.
 4. The AC-AC waveform transformationdevice according to claim 1, wherein the transformation module is abi-directionally semi-controlled m phase rectifying circuit, saidbi-directionally semi-controlled m phase rectifying circuit is formed byconnecting power semiconductor switching components or powersemiconductor switching component groups, the output polarity of saidbi-directionally semi-controlled m phase rectifying circuit is variable,said bi-directionally semi-controlled m phase rectifying circuitconsists of 2×m power semiconductor switching components or powersemiconductor switching component groups, each of the powersemiconductor switching component or power semiconductor switchingcomponent group is connected respectively between m input lines and twooutput lines.
 5. The AC-AC waveform transformation device according toclaim 2 or 3, wherein the power semiconductor switching component isbi-directional thyristor.
 6. The AC-AC waveform transformation deviceaccording to claim 2 or 3, wherein the power semiconductor switchingcomponent group is unidirectional thyristors which are positive-negativeconnected in parallel or IGBTs which are positive-negative connected inseries.
 7. The AC-AC waveform transformation device according to one ofclaim 2, 3 and 4, wherein the power semiconductor switching componentgroup is turn-off thyristors or IGCTs which are positive-negativeconnected in parallel or turn-off thyristors or IGCTs which arepositive-negative connected in series.
 8. An AC-AC waveformtransformation method, including the following steps: setting asine-wave voltage to be output, and dividing the sine-wave according totime interval t0, t1, t2, t3, . . . ti, and selecting the voltagewaveform during time t0˜t1 as the given reference voltage; selecting jgroups from n groups of m phases AC power supplies that are electricallyinsulated to each other as the current input voltage, where j≦n;performing bi-directionally controlled current rectification on the restn-j groups of m phases AC power supplies so that its output voltage is0; for the selected j groups of m phases AC power supplies that areelectrically insulated to each other, selecting one voltage waveform foreach group from all voltage waveforms output during t0˜t1 obtained aftercarrying out bi-directionally controlled rectification on j groups of mphases AC voltage so that j voltage waveforms are obtained bybi-directionally controlled rectification on the j group of m phases ACvoltage that are electrically insulated to each other; finding the sumof said j voltage waveforms and get a total calculated output voltage;comparing the calculated output voltage during t0˜t1 with said givenreference voltage; selecting m-phase AC power supplies of differentgroups from the above-mentioned n groups of m phase AC power suppliesthat are electrically insulated to each other as current input voltage;among each group of the m-phase AC power supplies, selecting differentvoltage waveforms on which gone through bi-directionally controlledrectification has been performed, so that the difference between thecalculated output voltage and given reference voltage is made as low aspossible at any time, and the total harmonics in the output voltage ismade the smallest or some high-order harmonics is made as low aspossible, or the total harmonics in the sum of current for n groups ofAC power supplies is made the smallest or some high-order harmonics ismade as low as possible; or the average leading or lagging power factorsof each supply in the n input groups is make as large as possible;determining the working status of each bi-directionally controlledrectifying circuit based on the voltage waveform corresponding to eachselected m-phase AC power supply, and performing bi-directionallycontrolled rectification in accordance to the working status determined;selecting the given expected voltage waveforms during time t1˜t2, t2˜t3,. . . ti−1˜ti as given reference voltages respectively, repeating step2˜8, and obtain the desired AC output voltage.
 9. The AC-AC waveformtransformation method according to claim 8, wherein said n groups of mphases AC power supplies that are electrically insulated to each otherare obtained by way of insulated transformation or insulated phase-shifttransformation of a total AC power supply.